I choose a design by FOSTEX with the full range unit driver FE206E which has been designed (according to the manufacturer) for use in back loaded horn type enclosures.

Although bass reflex projects have been presented by some manufacturers this driver is generally unsuitable for bass reflex enclosures because of its over dumping characteristics.

Building up the Horn speakers
In this project I build a ‘back loaded horn’ type enclosure following the exact designing instructions from FOSTEX, and I used the FE206E unit.
In this specific DIY horn speakers project I chose for building up the speaker cabinets a type of Finnish birch plywood 21mm thick (15 plies of hardwood veneered plywood layers) for the main section and side panels, which has a sound reduction index more than 23.8 dB according to the manufacturer.
Also I used Dynamat for extra sound absorbency; we coated the place behind each driver unit. The total weight of each speaker is more than 55 kilograms!
The result, however, is a well damped and non resonating enclosure.

Click on the image to Download the enclosure schematicChoosing plywood as a material

Plywood is made by slicing wood into thin veneers and gluing the veneers together to form a sheet.
Its high strength, stiffness and surface dimensional stability make it ideal for making speaker cabinets.
Its cross-laminated construction also, ensures that plywood sheet sizes remain relatively stable under changes of temperature and moisture, making it particularly suited to form work applications like loudspeakers cabinets.
Generally though its construction is difficult and requires very good work (woodworking) the result will compensate you!
Read a loudspeaker review, and watch a video of my DIY loudspeakers here